GENERAL LAWS OF ORIGIN AND MIGRATION. 269 



In a recent address, delivered to the biological section 

 of the British Association, Mr. Carruthers has discussed 

 this question, and has shown that the earliest vegetable 

 specimens described by Dr. Schweinfurth from the Egypt- 

 ian tombs present no appearance of change. This fact 

 appears also in the leaves and other organs of plants pre- 

 served in the nodules in the Pleistocene clays of the Ot- 

 tawa, and in specimens of similar age found in various 

 places in Britain and the continent of Europe.* 



The difficulties attending the ordinary theories of 

 evolution as applied to plants have been well set forth by 

 the same able botanist in his "Presidential Address to 

 the Geological Association in. 1877," a paper which de- 

 serves careful study. One of his illustrations is that 

 ancient willow, Salix polaris, referred to in a previous 

 chapter, which now lives in the arctic regions, and is 

 found fossil in the Pleistocene beds at Cromer and at 

 Bovey Tracey. 



He notes the fact that the genus Salix is a very varia- 

 ble one, including 19 subgeneric groups and 160 species, 

 with no less than 222 varieties and 70 hybrids. Salix 

 polaris belongs to a subgeneric group containing 29 

 species, which are arranged in four sections, that to 

 which S. polaris belongs containing six species. Now it 

 is easy to construct a theoretical phylogeny of the deri- 

 vation of the willows from a supposed ancestral source, 

 but when we take our little 8. polaris we find that this 

 one twig of our ancestral tree takes us back without 

 change to the Glacial period. The six species would take 

 us still farther, and the sections, subgenera, and genus 

 at the same rate would require an incalculable amount of 

 past time. He concludes the inquiry in the following 

 terms : 



* "Proceedings British Association," 1886, "Pleistocene Plants of 

 Canada,' 1 Canadian Naturalist, 1866. 



